A Jordanian state security court convicted a former top aide to King Abudullah II and a member of the royal family on Monday for plotting a coup against the monarchy.
The two men were also sentenced to 15 years in prison.
Bassem Awadallah, a US citizen and former top aide to the king, and Sharif Hassan bin Zaid, a member of the royal family, were found guilty of incitement and sedition charges.
They were arrested in April over the allegations they collaborated with Abdullah's half-brother Prince Hamzah to foment unrest.
Hamzah has only made rare public appearances since the accusations came to light earlier this year.
The 41-year-old claimed that he had been placed under house arrest, saying he was being silenced for speaking out against corruption.
But the Jordanian royal family denied Hamzah's claims at the time, but says it has resolved its dispute with the former crown prince.
What does the defense allege?
Awadallah has hired a former federal prosecutor, Michael Sullivan, to represent him.
Sullivan accuses the Jordanian state of torturing his client, including electric shocks, to force a confession and that a guilty verdict appears to be a foregone conclusion.
The US lawyer said the trial before Jordan's state security court "has been completely unfair," meeting behind closed doors on only six occasions.
He said that Jordanian lawyers have been denied the chance to call witnesses or see all the evidence against Awadallah.
But Jordanian prosecutors told the Associated Press news agency that he would be "guaranteed due process" in line with the law.
"He has not been mistreated in any way, and his allegations of torture of any kind are false," they said in a statement.
Both defendants have pleaded not guilty to sedition and incitement charges, which carry lengthy prison terms.
King Abdullah II is one of the United States' closest allies in the region and receives $1.27 billion (€1.07 billion) in aid from Washington each year, the majority of which is spent on defense and security.
The monarch will meet with US President Joe Biden on July 19 and is seen as a key partner in eventually reviving the Israeli-Palestinian peace process.
Awadallah, who also holds Jordanian and Saudi citizenship, served as head of the royal court and government minister in Jordan.
His family have urged Biden to demand his immediate release in his talks with Abdullah.
Who is Prince Hamzah?
The 41-year-old is the oldest son of the late King Hussein and Queen Noor.
He attended the elite Harrow School and the Royal Military Academy at Sandhurst in the United Kingdom.
Hamzah has been widely tipped to succeed King Hussein prior to his death.
But when Hussein passed away in 1999, he was overlooked in favor of his older half-brother, Abdullah.
Abdullah stripped Hamzah of the title of crown prince in 2004.
jf/rs (AFP, AP)